Fluid coking reactor and process



March 31, 1959 w.w. BOISTURE 2,830,169

' FLUID COKING REACTOR AND PROCESS Filed Feb. '10, 1954 2 Sheets-Sheet 1FROM BURNER RISER GAS' T FEED STEAM TO BURNER FIGURE I Worth W. BoIsture Inventor March 31, 1959 y w. w. BOISTURE 2, FLUID coxmc: REACTORAND PROCESS.

Filed Feb. 10, 1954 K- 2 Sheets- Sheet 2 FROM BURNER TO BURNER I coxsFIGURE -1I[ Worth W. Boisfure Inventor By L'WAHorney over of solidparticles from the fluid bed.

Worth. reins... R908 1-8., nssiguor to Esso ltes'earchandffilngin eCompany, a corporation of ApplicatioufFebi-uary 10, 1954, Serial No.409,476

[7 Claims. or. 208-157) the oil undergoes pyrolysis in the fluidizedbed, evolving lighter hydrocarbons and depositing carbonaceous residueon the solid particles. ,The necessary heat for the thermolysis issupplied by circulating a stream of the fluidized solids through anexternal heater and back to the coking vessel. The solids, which havehad carbon deposited on them during the coking, are partially combustedin the heater. It can be seen that this technique of fluidized cokingoffers a great advantage over the delayed coking process in that theoperation is continuous. This fluid coking process is more fullypresented by co-pending application,- titled, Fluid Coking of HeavyHydrocarbons and Apparatus Therefor," S.N. 375,088,

filed August 19, 1953, by Pfeiffer et al.

' Serious problems, however, have been encountered in the development ofthis type of coking. One particular problem is the building up of cokedeposits on the confines of the vapor space above the fluidized bed andin lines removing the hot vapors from the coking vessel. It has beenfound that the high boiling constituents in the hot coker vapors willreadily condense and that if this condensation is on surfaces having atemperature of about 700 to 1000 F., severe coking will occur withconsequent fouling and plugging of the equipment. This coke depositionhas been inhibited somewhat in prior fluid coking processes by providingfor entrainment and carry This has been accomplished by increasing thevelocity of the gases in the dilute phase above the fluidized solids bed(by decreasing the reactor cross-sectional diameter at this point) orby-causing the internal solids-gas separator or cyclone to operateinefliciently, as by aerating the cyclone dipleg. The entrainedparticles help uphold the temperature of the vapors, scour attendantsurfaces, thereby removing carbon deposits, and provide surfaces uponwhich condensing vapors are absorbed. This method, however, has not beenentirely satisfactory. Larger amounts of fluidizing gas have to be usedto cause the entrainment and this undesirably dilutes the vapors andincreases the size carbon vapors but this requires additional heatingand V compressing capacity for the diluent besides increasing the loadon subsequent separation equipment.

$380,169 Patented Mar. 31, 1959 lem of coke deposition. It is an objectof this invention to provide an improved fluid cokng process andapparatus which successfully overcomes this and other problems. Otherobjects and advantages will appear more clearly in the followingdescription in which the attached drawings, forming a part of thisspecification, are discussed in detail.

Figure l of the drawings discloses one embodiment of the inventionincorporated into a conventional fluidized solids bed, hydrocarbon oilcoking vessel. Figure 2 is a sectional view of the apparatus of Figure 1taken along line lI-II of Figure 1. Figure 3 is second embodiment of theinvention.

Generally, the objects of this invention are attained by placing aconcentric bathe in the upper or dispersed phase zone of'a fluid cokingreactor radially spaced from the internal reactor wall and extendingdownwardly below the pseudo-liquid level of the fluidized bed. Hotsolids, returning from an external combustion zone or burner, areinjected tangentially into the annulus formed by the baflie and theouter vessel walls. in this manner an internal conduit of reduceddiameter is formed through which a major portion of the hot efliuentcoker vapors pass. The hot tangentially injected solids, which have atemperature of about l000'1500 F., maintain the temperature of thebaffie above the condensation point of the vapors and thereby cokedeposition in this zone is prevented. Tangential injection of the heatedsolids is used not only to distribute the solids throughout the annulus,but also to accomplish centrifugal solids-gas separation in that zone.

This arrangement has several decided advantages aside from preventingcoke deposition. The most obvious is the combination of the solidsseparator and the top section of the reactor whereby a vessel ofsubstantially constant external diameter can be formed which would lowerfabrication and construction costs in commercial units.

Another very definite advantage is that this design reduces thecross-sectional areaof the passageway for the product vapors. This tendsto keep coke entrainment reasonably high without excessively highfluidizing gas rates in the dense bed and reduces vapor holding timethereby minimizing vapor phase cracking.

Referring now to the drawings, a simplified cross-sec- A heavyhydrocarbon oil such as 12.9% West Texas vacuum residuum along withrecycled bottoms from the coker efiluent fractionator is introduced intothe coker from manifolds 6 by lines 7 at a rate of 0.1 to 3 weight ofoil per weight of solids in the fluid bed. To avoid bogging andagglomeration of the bed, it is preferred that the feed be sprayed orinjected into the bed at a multiplicity of points both circumferentiallyand vertically. In the hot fluid bed, the oil is converted at atemperature of 900 to 1200 F., preferably 950 F.,to carbonaceous residuewhich is deposited on the fluidized solids and hot hydrocarbon vapors.The vapors pass upwardly, with some entrainment, past the pseudo-liquidlevel of the bed L to a gas-solids separator, e.g. a cyclone 3, where 1a portion or substantially all of the entrained solids are Thisinvention is concerned primarily with this probremoved and returned tothe bed by line 4. Inclined baffles, vanes or the like may besatisfactorily used in place of the cyclone in some applications.Product vapors are removed from the coker by line 5 and tram- 3 ferredto subsequent operations such as fractionation or quenching, not shown.

Fluidizing gas, e.g. steam, is admitted at a plurality of points in thelower portion of the coker, one of which is shown as line 12. This gaswill amount to about 5 to 30 weight percent of the liquid hydrocarbonfeed and serves not only to maintain the fluidity of the solids bed, butalso to strip the particulate solids of hydrocarbon vapors before theyare transferred to the combustion zone by line 8.

Normally coke will be produced in excess of that required to supply heatfor the thermolysis and this excess is removed by line 14 as product.There will also be removed by this line particles that have increased insize by reason of the carbon deposition, or because of agglomeration ofthe particles, to the extent of being unfluidizable.

A portion of the bed is continuously removed by line 8 and transferredto a combustion zone, not shown. This zone can be one of several types.A vessel containing a fluidized bed of the solids, fluidized by air tosupport combustion, is preferred but a gravitating bed, a transfer lineburner or other combustion equipment would suffice. A portion of thecarbon deposited on the solids in the coking zone is burnt ofi in thecombustion zone, raising the temperature of the remaining particles to atemperature of 1000 to 1500 F., preferably 1l00 to 1300 F. The hotsolids are returned to the coker by line 9. This method of combustionof. carbon-containing solids and of transferring solids between zones iswell known per se and, therefore, an elaborate description has not beenmade of these techniques.

For this example, the returned solids are shown as being tangentiallyinjected at a plurality of points, e.g. 3. at the top of the reactor.Whether one point of injection or more is used will depend upon theequipment design, e.g., the diameter of the top of the coker, amount ofsolids circulation, and the radial depth of the annulus.

As depicted, the returned hot solids in line 9 are divided into 3streams bylines 10 and tangentially introduced into the annulus (seeFigure 2) formed by battle 2 and vessel wall 11. The conveying gasseparates from the heated solids and this separation is aided by thecentrifugal force created by the tangential injection of the solids. Thehot solids move downwardly and enter the conical section or main fluidbed and the conveying gas passes through line 5 with theproduct vapors.

It is customary in normal coking operations to admit a conveying oraerating gas, generally steam, to the upwardly flowing solids in thetransfer lines at one or more points. Line 13 admits such a conveyinggas to transfer line 9. By judicious control of the amount of gasadmitted, it is possible to control the amount of entrained solidcarried over in line 5. By the design of this invention, the hot solidsfrom the burner, which are at a higher temperature than the main fluidbed, are preferentially entrained. Because of the higher temperature ofthe entrained solids in the method of this invention, a lesser amount ofsolids are needed than in the conventional operation to prevent cokingof the transfer lines of the hot coker vapors. The vapors are maintainedabove their condensation or dew point by the solids and consequentlycoking is greatly inhibited.

Thus, it can be seen, that by this invention, a major portion of the hotcoker gases are made to pass through the central conduit formed by thebaffle and the surfaces of the bafile are maintained above the dew pointof the vapors. By this means, coke deposition on the reaction vesselwalls is prevented. Because the vapors pass through the narrowpassageway formed by the baffle, vapor residence time is held to aminimum. Further, bccause hot solids from the burner are preferentiallyentrained and because the amount of solids entrainment is easilycontrolled, coke deposition in vapors handling lines leading from thecoker is inhibited.

The coking operation is usually carried out at relatively low pressure,such as from 0 to 50 pounds per square inch guage. It is preferred tooperate at a vapor outlet pressure sufiicient to force the vaporsthrough subsequent fractionating and separating equipment.

Figure 3 illustrates another form of a coking reactor 51 having a baflie54 designed according to this invention. The main difference betweenthis design and that of Figure 1 is that the coker vapor-solidsseparator or cyclone 56 is external from the coker 51. Briefly, feed isconveyed to the reactor by line 52 and injected at a plurality of pointsby lines 53. Fluidizing and stripping stream is admitted at a pluralityof points in the lower portion of the reactor by lines 62. Product cokeis removed by line 61 at the base of the reactor. The hot coker vaporspass upwardly through the conduit formed by bafile 54 and are removedfrom the coking vessel by line 55 to cyclone 56. Here entrained solidsare removed and returned to the main fluid bed by line 58. The vaporsare taken from the cyclone by line 57 to further processing, not shown.It is to be understood that the cyclone 56 can be so operated to permitsolids carry over into line 56 and subsequent equipment. One method forcontrolling this entrainment is to pass gas into standpipe 58 by line65. As before mentioned, this solids entrainment may be desired in orderthat the solids may maintain the temperature of vapors, scour attendantsurfaces and provide surfaces for coke deposition.

Particulate carbon containing solids are removed by line 59 andtransferred to a combustion zone, previously described in connectionwith Figure 1. The heated solids are returned from the combustion zoneby line 60 and tangentially introduced into the annulus formed byinterior. baffle 54 in the upper portion of the reactor.

A variation is shown by the drawing in that the riser" or conveying gasof the circulated solids is not used to control the amount of hot solidsentrainment. a gas, for example steam, is admitted to the lower portionof the annulus by lines 63. By controlling the amount of gas admitted,the'amount of entrainment of solids is readily controlled.

It will be apparent to those skilled in the art that this invention iscapable of various modifications and applications. Consequently, theinvention is not to be limited by the above description, but only by thefollowing claims.

What is claimed is:

1. A process for the conversion of heavy hydrocarbon oils, whichcomprises injecting a multiplicity of streams of said heavy oil into anenlarged circular coking vessel containing a body of finely dividedsolids having a pseudoliquid level at the upper portion of said vessel,circulating said solids to an external heating zone, circulating heatedsolids from said heating zone to said coking vessel, tangentiallyinjecting said heated solids into an annulus in the upper portion ofsaid vessel above the level of said body of solids to maintain saidvessel at a coking temperature between 900 and 1200 F., said annulusbeing formed by an internal concentric baflle radially spaced from theinternal wall of said upper portion of said circular coking vessel, saidbaffic extending downwardly below said pseudo-liquid level and forming acentrally located conduit, passing gaseous material upwardly throughsaid coking vessel at a velocity sufiicient to maintain said body ofsolids in a dense turbulent fluidized state, maintaining said oil withinsaid coking vessel for a period sufficient to convert the same intovapors and coke, and withdrawing vapors so formed from the top of saidvessel through said centrally located conduit.

2. An apparatus for the conversion of heavy hydrocarbon oils comprisingan enlarged circular coking vessel adapted to contain therein a denseturbulent bed of fluidized solids having a pseudo-liquid level. near theupper portion of said vessel, a plurality of nozzles passing Instead 7through the walls of said vessel, means for introducing said oilsthrough said nozzles, a dense turbulent body of 5 fluidized solidswithin said vessel having an internal coni centric battle in the upperportion of said vessel radially spaced from the internal wall of saidcoking vessel to form an annulus, extending downwardly below the upperportion of said vessel and below said pseudo-liquid level and forming acentrally located passageway for upwardly 5 moving vapors, the bottomterminal cross section of said battle being of greater area than theupper portions of said cross-section, injecting a heavy hydrocarbon oilinto said bed to form vapors and coke which is deposited on said solids,withdrawing overhead said vapors through a confined passageway ofreduced diameter, said confined passageway forming with the confines ofthe upper portion of said coking zone an annular passageway extendinginto said bed, circulating a portion of said bed to an external heatingzone, tangentially introducing heated solids from said heating zonealong with conveying gas into said annular passageway whereby the wallsof said confined passageway are maintained above the dewpoint of saidvapors, passing heated solids from said annular passageway to said bed,and passing said conveying gas upwardly through said annular passageway,and mixing thereafter 3. The apparatus of claim 2 comprising in additionthereto conduit means for admitting gas to the lower por-. tion of saidannulus. 4. The apparatus of claim 2 wherein said heated solids aretangentially introduced into said annulus at a plurality 5 of points.

5. The apparatus of claim 2 comprising in addition thereto gas-solidsseparating means located in said centrally located passageway for thepurpose of removing entrained solids from said vapors."

6. An improved fluid coking process which comprises maintaining a denseturbulent bed of fluidized particulate solids at a coking temperature ina coking zone of circular gases from said annular passageway with saidvapors withdrawn overhead.

7. The process of claim 6 wherein heated solids are en trained from saidannular passageway and commingled with said vapors withdrawn overhead.

kelerenoescltsdintheflleotthis patent UNITED STATES PATENTS 2,289,329Prickett July 7, 1942 2,394,651 Alther Feb. 12, 1946 2,444,990 HemmingerJuly 13, 1948 2,661,324 Lefier Dec. 1, 1953 2,706,704 Squires Apr. 19,1955 2,719,112 Kearby Sept. 27, 1955 2,719,818 Findlay Oct. 4, 19552,763,601 Martin et al Sept. 18, 1956 2,791,549 Iahnig -2 May 7, 1957

1. A PROCESS FOR THE CONVERSION OF HEAVY HYDROCARBON OILS, WHICHCOMPRISES INJECTING A MULTIPLICITY OF STREAMS OF SAID HEAVY OIL INTO ANENLARGED CIRCULAR COKING VESSEL CONTAINING A BODY OF FINELY DIVIDEDSOLIDS HAVING A PSEUDOLIQUID LEVEL AT THE UPPER PORTION OF SAID VESSEL,CIRCULATING SAID SOLIDS TO AN EXTERNAL HEATING ZONE, CIRCULATING HEATEDSOLIDS FROM SAID HEATING ZONE TO SAID COKING VESSEL, TANFENTIALLYINJECTING SAID HEATED SOLIDS INTO AN ANNULUS IN THE UPPER PORTION OFSAID VESSEL ABOVE THE LEVEL OF SAID BODY OF SOLIDS TO MAINTAIN SAIDVESSEL AT A COKING TEMPERATURE BETWEEN 900* AND 1200* F., SAID ANNULUSBEING FORMED BY AN INTERNAL CONCENTRIC BAFFLE RADIALLY SPACED FROM THEINTERNAL WALL OF SAID UPPER PORTION OF SAID CIRCULAR COKING VESSEL, SAIDBAFFLE EXTENDING DOWNWARDLY BELOW SAID PSEUDO-LIQUID LEVEL AND FORMING ACENTRALLY LOCATED CONDUIT, PASSING GASEOUS MATERIAL UPWARDLY THROUGHSAID COKING VESSEL AT A VELOCITY SUFFICIENT TO MAINTAIN SAID BODY OFSOLIDS IN A DENSE TRUBULENT FLUIDIZED STATE, MAINTAINING SAID OIL WITHINSAID COKING VESSEL FOR A PERIOD SUFFICIENT TO CONVERT THE SAME INTOVAPORS AND COKE, AND WITHDRAWING VAPORS SO FORMED FROM THE TOP OF SAIDVESSEL THROUGH SAID CENTRALLY LOCATED CONDUIT.